Means for manufacturing pressed powder bodies

ABSTRACT

A pressed powder body is formed by introducing powder into a space on the outside of a mandrel and inside a rubber sleeve to the outside of which fluid under pressure is supplied. Punches move downward from above and upward from below into the space between the mandrel and sleeve to precompact the powder.

References Cited UNITED STATES PATENTS 4/1939 Jeffery..........................

United States Patent Inventor Hans Lundstrom Robertsfors, Sweden [21 1 Appl. No. 693,626

5x5 W56 1 00 l 2,152,738 gl d d g 2,937,421 5/1960 Taccone....................... aeme 1 3,034,191 51962 Schaeferetal............... [73] Assignee Allmanna SvenskaEleklriskaAktiebolaget 3,172,153 311965 Loomis etalmm vasteraesweden 3,193,900 7/1965 Wendt..... [32] Pnorlty Dec. 27, 1966 3,200,442 8/1965 Haller...... Primary Examiner-J. Howard Flint, Jr. Attorney-Jennings Bailey, Jr.

IS/16.5, l8/5,264/l09 l3 3] Sweden [54] MEANS FOR MANUFACTURING PRESSED POWDER BODIES 1 Claim, 5 Drawing Figs.

ABSTRACT: A pressed powder body is formed by introducing powder into a space on the outside of a mandrel and inside a tside of which fluid under pressure is [51] Int. B29c3/00, r ber sleeve to the ou supplied. Punches move downward from above and upward and sleeve to [50] Field of 18/5 (I), 5 rom below into the space between the mandrel (M) (Cursory), 16.5 (Cursory) precompact the powder.

PATENTEUMARNIQ?! 357L 54 sum 1 BF 2 v Fig 0 Fig. 1 4 I I INVENTOR. HA N zvu/u os'TRdM PATENTED HAR23 um SHEET 2 OF 2 Page k 1 7 u WEN An a 5 3 Ada H Lump sT/wm INVEN TOR.

MEANS FOR MANUFACTURING PRESSED POWDER BODIES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for manufacturing pressed powder bodies, which device comprises a punch to be pressed axially into a mould space surrounded by a pressure cylinder and limited in axial direction by the end surface of an expelling punch.

With such known devices it is difficult to achieve the same density in the different parts of the pressed body.

2. The Prior Art According to a known method the powder is compressed by filling a mould having resilient sidewalls and then closing the mould with a tightly fitting lid. The mould is then placed in a pressure chamber to which pressure medium is supplied in a quantity corresponding to the volume decrease of the powder body caused by compression. This method, which gives a relatively high degree of homogeneity in the product, is hardly practicable when a high speed production rate is required, since there are many time-consuming steps involved.

SUMMARY OFTIIE INVENTION supporting means and said hollow body are arranged to be surrounded by a container containing pressure medium which acts with variable pressure on the outside of said hollow body, that said lower annular supportinglmeans is closed by means of an upwardly operating lower punch after which the required quantity of powder and then a downwardly operating v upper punch are inserted in said upper annular supporting means, whereafter the powdered material is compressed by means of said punches and the pressure simultaneously increased in said pressure chamber, after which the pressure is again reduced, the downwardly operating upper punch removed, and theupwardly operating lower punch moved upwards so that the finished product is expelled.

A device according to the invention comprises a punch to be pressed axially into a pressure cylinder the upper part of which has a greater inner diameter than the lower part and tightly surrounds a flange-shaped top portion of a tubular piston, the lower part of which is tightly surrounded by, said lower part of the pressure cylinder, whereas said tubular piston surrounds an expelling means which provides a surface for axial limitation of a mould space surrounded by the tubular piston characterized in that an annular space formed between said cylinder and said tubular pressure piston is filled with a pressure medium which, through radial, through-running space II which is radially internally limited by a central cylindrical core 3. When a powder with very poor flow properties is used, the lower stamp 4 may be drawn down and pushed up again while the charging tube remains over the opening. The charging tube is moved to the side to a stand not shown in the drawing and smooths away superfluous powder. The upper punch l (downwardly and upwardly movable) is pressed downwards. When this touches the powder surface, the lower punch 4 moves upwards with the same speed so that the powder is precornpacted to a certain extent in axial direction (FIG. c). During the continued movement of the upper stamp the parts 38 are forced downwards. In the partly perforated, tubular supporting member 6, a hollow resilient wall 7, for example a rubber tube having upper and lower openings is attached at its upper and lower ends with the help of annular grooves 8 in the annular supporting parts of the tubular supporting member. The tube rests with its outer surface against a perforated part of the member 6, and through the perforachannels, communicates with radially outer side of a resilient tube arranged on the inner side of said hollow piston, said tube being tightly attached by its ends to said tubular piston.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. a, a charging tube 2 with the powder to be pressed has been moved over the tool. The lower punch 4 (upwardly and inwardly movable) is drawn down while the charging tube vibrates (FIG. b). The powder is then drawn down and fills the tions, can be acted on by a pressure medium within the container It The space 9 is closedby seal 5. When the piston 6, together with the other parts, is forced downwards, the space 9 is decreased and the pressure medium (oil, water or the like) is pressed in through the perforations and forces the tube 7 of the piston to contract radially inwards towards the powder mass 11, thus performing an isostatic pressing (FIG. d). When the desired pressure has been reached, theupper punch moves upwards and the parts 3, 5, 6 and 7 return to the same position as in FIG. 0. The resilient tube 7 then extends radially towards the piston 6 (also due to outer underpressure generated if the space 9 is not completely filled with fluid pressure medium). The lower punch 4 then moves upwards and expels the finished tube-shaped product (FIG. e). The expulsion force is very low since elastic expansion of the pressed tube prevents attachment to the core 3. The charging tube 2 is then moved to the position shown in FIG. a and simultaneously pushes the finished product to the side, and the pressing cycle is repeated.

The described pressing process is similar to conventional nonisostatic powder pressing as regards the most time-consuming stages, for example the powder filling, and thus substantially the same rate of production can be achieved. Parts with large height-width ratio, even of ceramic material, can in the described tool be pressed to a high and uniform density.

The necessary punching force is relatively low since the pressure medium acts on the punch axially only on the upper surface of the space 9, while the outersurface of the tube 7 can be very large. With suitable outer diameter the tool can economically be used even for very high pressures, 10 to 15 kb 10 to l5 ton/cm and for very large powder structures.

The example shown in the drawing is a simple tubular work piece, but a device according to the invention is also suitable for other shapes, for example tubes with varying inner and outer diameter, work pieces having noncircular cross section and solid work pieces. The described axial precompacting is not always necessary either.

I claim:

i. A device for manufacturing pressed powder bodies, which comprises a tubular supporting member having upper and lower annular supporting parts, a resilient wall comprising a relatively thin hollow body having upper and lower openings arranged within the tubular supporting member and attached around said openings to said upper and lower annular supporting parts, a container having means forming a pressure medium space therein on the outside of said hollow body surrounding said tubular supporting member and said hollow body, an upwardly and downwardly movable lower punch closing the lower end of said tubular supporting member, a downwardly and upwardly movable punch movable into the upper end of said tubular supporting member, said container and said tubular supporting member together comprising a means responsive to movement of said punches towards one another for reducing the pressure medium space within said container so as to increase the pressure of the pressure medium on said resilient wall. 

1. A device for manufacturing pressed powder bodies, which comprises a tubular supporting member having upper and lower annular supporting parts, a resilient wall comprising a relatively thin hollow body having upper and lower openings arranged within the tubular supporting member and attached around said openings to said upper and lower annular supporting parts, a container having means forming a pressure medium space therein on the outside of said hollow body surrounding said tubular supporting member and said hollow body, an upwardly and downwardly movable lower punch closing the lower end of said tubular supporting member, a downwardly and upwardly movable punch movable into the upper end of said tubular supporting member, said container and said tubular supporting member together comprising a means responsive to movement of said punches towards one another for reducing the pressure medium space within said container so as to increase the pressure of the pressure medium on said resilient wall. 